Flue cap



F. ALWARD FLUE CAP April 24, 1956 2 Sheets-Sheet Filed Oct. 16, 1953fnventar', Fran 0035' A Zward,

April 24, 1956 F. ALWARD 2,742,846

FLUE CAP Filed 001;. 16, 1953 2 Sheets-Sheet 2 Fz'y. 3. 4\ /2 /4Inventor, Francis A Zward United States Patent I F FLUE CAP FrancisAlward, Cambridge, Mass.

Application October 16, 1953, Serial No. 386,435

3 Claims. (Cl. 98-84) This invention relates to flue caps and is moreparticularly concerned with a new and improved attachment for theoutlets of flues and ventilators or the like which will effectivelyprevent down drafts while still permitting free escape of the air orgaseous mixture irrespective of the angle or direction of the wind.

Various expedients have heretofore been proposed for preventing downdrafts in the fiues of chimneys and in various ventilating pipes whilesimultaneously preventing the entry of rain and snow but not interferingin any way with the draft. Any attachment which can be devisednecessarily interferes to some extent with the free exit of air or gas,the ideal situation apart from the down-draft problem being a completelyfree opening. Most attachments which have heretofore been proposed haveinvolved moving parts with specially designed louvers which must face atall times in a predetermined direction with refererence to the wind. Sofar as I am aware, no completely effective flue cap for this purpose hasso far been devised which, while furnishing negligible interference tothe free flow of the escaping gas or air, nevertheless effectivelyprevents down drafts, no matter which way the wind is blowing, and whichrequires no moving parts.

In this specification and the accompanying claims, I will term the noveldevice a flue cap, it being understood that the term flue embraces anygas or air outlet, whether mounted on a building, motor vehicle, train,ship, airplane, or elsewhere.

With the foregoing in mind it is an object of my invention to provide anew and improved flue cap for preventing down drafts in flues, the novelcap having no moving parts and operating effectively no matter what theangle or direction of the wind.

It is a further object of the invention to provide a flue cap of thetype described which is simple, rugged and enduring in construction,economical to manufacture, and which is adaptable for use on flues ofany size or shape.

It is a further object of the invention to provide such a flue cap whichwill operate effectively while presenting a minimum obstruction to thefree escape of air or gas from the flue on which it is mounted.

My novel flue cap comprises a series of relatively thin plates,preferably of metal, mounted in a vertically arranged stack in generallyhorizontal parallel spaced relation. All of the plates, with theexception of the uppermost, are provided with central openings which arepreferably aligned with each other and which correspond generally insize with the dimensions of the flue which is to be capped and whichtogether form a central cavity in the cap, into which open a pluralityof passageways from all sides formed by the intervals between theplates. At the base of the stack of plates I preferably attach a shortsection of conduit or piping or other mounting portion suitable forattaching the assembly to the flue or chimney on which it is to bemounted. One or more of the lowermost plates comprise a lower platesection so shaped and proportioned, as by having one or more inner.edges bordering the central openings turned upwardly, or other.-

ing plates to. prevent entry of rain or other precipitation or downdrafts from above. The upper section is composed of a sufiicient numberof plates, in view of their di-.' mensions and spacing, to provide atotal passage for the. escape of air or gas at least equal to thecapacity of the flue to be capped. I

The foregoing and other objects, features and. advantages of theinvention will become apparent from the following detailed descriptionof presently preferred embodiments thereof taken in conjunction with theaccom-' panying drawings in which like numerals refer to similar partsin the several views, and in which Fig. l is a front elevation withportions broken away and partly in section of a circular novel flue capaccording, to the invention; t

Fig. 2 is a view partly in plan and partly in section of the same takenon line 22 of Fig. l;

Fig. 3 is a top plan view with a portion of. the upper plate broken awayillustrating a modified square form of.

the invention; and

Fig. 4 is a sectional view of the embodiment shown in' Fig. 3 taken online 4-4 of Fig. 3.

Referring first to the embodiment of Figs. 1 and 2, the

novel flue cap of the invention is indicated generally by the numeral10. It comprises a series of stacked plates,

of metal or suitable substitute material, forming upper and lower platesections of special shape, as hereinafter described. The top plate 12 isa solid disc except for mounting holes and it serves as a cover or lidfor the flue cap excluding precipitation and the entry of down draftsfrom above. The next lower plates which comprise the balance of theupper plate section and are indicated by the numerals 14 and 14a, areplane and have central openings 16 and 16a which are aligned with eachother. The lowermost plates 18 forming the lower plate section are alsoprovided with central openings 20 and their inner edges adjacent theopenings are uniformly turned upwardly, as at 22, the edge of the flangethus formed on the uppermost plate 18 preferably lying in the plane ofthe lowermost plate 14a of the upper plate section. The intervalsbetween the plates form air passageways between the interior andexterior of the cap.

It will be noted that the central openings in the plates 14 and 14a areslightly larger than the openings 20. As a matter of principle, it isonly necessary that the opening in the plate 14a be somewhat larger thanthe opening in the next lower plate in order to leave a ring-likeaperture between the turned up edge 22 and the inner edge of the plate14a for the passage of air. The opening 16 in the remaining plates 14might be of any'suitable' size so long as the critical formula mentionedbelow is adhered to. As a matter of convenience and economy ofmanufacture I prefer to make all the plates 14 and 14a identical insize.

The plates 12, 14, 14a and 18 are held in a vertical stack in spacedapart generally horizontal and parallel Patented Apr. 24, 19.5.6

At the. base of the two plate sections, there is aflixed, by welding orotherwise, a pipe or conduitsection. 28 or other connecting element ormounting portion which is of suitable size and shape for attaching thenovel flue cap to the particular flue.

As indicated by the broken line x-x, it is impossible to draw anunobstructed straight line at any level of the flue cap which touchesthe outer edge of a plate and the inner edge of the next lower plate andwhich will terminate at a point below the lowermost air passageway intothe interior of the cap which, in this embodiment, is defined by theopposing surfaces of the two lowermost plates 18 and their respectiveflanges. Such a line thus must impinge above the top of the pipeextension 28. In fact, in the particular construction shown, this lineimpinges upon the turned up flange 22 of the plate 18 which is the thirdfrom the bottom of the stack. Any line drawn below the line x-x mustimmediately hit one of the tip-turned flanges 22 and cannot passunobstructed into the center of the flue cap. Similarly, any line abovethe line x-x, as the line yy, for example, which passes unobstructedinto the central cavity of the cap, impinges upon the inner edge of astill higher plate than that hit by the line x-x, in this case upon theplate 14a.

The importance of the foregoing geometrical arrangement becomes apparentif one supposes a very narrow downwardly inclined external current ofair striking the flue cap as indicated by the arrow W in Fig. 1. Such acurrent would, without any special flue cap, produce a down draft in thepipe extension 28. It will be evident from the geometry of my novel capthat the continuing downward movement of any infinitely narrow currentof air produced by the wind W, after passage into the flue cap, islimited to the angle of the line x--x. Thus if we assume such aninfinitely narrow current of air (comparable to a straight line)impinging upon the novel flue cap at any level on the left-hand side ofFig. 1, clearly it is impossible for such a current of air to passthrough one side of the cap into the center with any remaining downwardcomponent suflicient to cause a down draft. Such an inclined current ofair, for example, striking between the plate 14a and the next lowerplate (or between any of the plates below such next lower plate) will beturned upwardly by the upwardly directed flanges 22, as indicated by thearrows. Similarly, any downwardly inclined current of air arriving atthe flue cap on the lefthand side at or above the line xx and at thesame or a steeper angle will at once be straightened at least to theangle x--x by passage between the plates 14 and, at a this angle, itcannot pass down the pipe 28 since it will, upon arriving at theopposite side of the flue cap, strike an up-turned flange 22 and eitherbe directed upwardly within the flue cap or outwardly between theflanges 22 to the exterior.

It is also clear that external currents of air striking the flue cap ata less steep angle than that of the line xx will pass between theseveral plates and will have even less of a tendency to cause any downdraft. Horizontal air currents will, of course, pass directly betweenthe upper plates 14 as indicated by the line zz and during their passageout the other side will draw with them air or gases coming up into theflue cap from the pipe 28. Any portions of such currents passing betweenthe inwardly flanged plates 18 will be turned upwardly within the fluecap and the remainder will be diverted exteriorly of the inner sectionof the cap.

A particular advantage of the construction of my novel cap is that anyflow of air around its exterior in any direction, particularly aroundthe outer sides of the curved flanges 22, tends to draw the air or gasfrom within, thus inducing or increasing the desired up-draft within theflue on which it is mounted. A similar effect is also caused by any flowof air past the outer edges of the plates 12, 14, 14a or 18 that doesnot pass between them into the interior. of the cap.

In view of the fact that the geometry of the fiue cap is symmetrical inall directions, the flue cap will operate no matter from which directionthe wind is coming and there is no need for moving parts to turn thenovel device with the wind. I have found that a flue cap as illustratedin Figs. 1 and 2 will operate with great effectiveness on the lines ofchimneys where adjacent structures, hills or trees may producedownwardly directed air currents and likewise it will operate withunusual effectiveness as a cap for ventilators which merely serve thepurpose of exhausting air from within buildings. The flue cap, accordingto the invention, is also adaptable and highly effective for use onventilators or flues of moving trains, motor vehicles, ships, boats, oraircraft, etc., operating with great effectiveness whether or not thevehicle is in motion and requiring no orientation with respect to thewind.

Another embodiment of the invention is illustrated in Figs. 3 and 4 inwhich the plates of the previous embodiment are shown as non-circular,in this case rectangular or square in configuration with square centralopenings. The plates, flanges, bolts and openings all functionidentically as in the previous embodiment and have therefore been giventhe same numerals. The reference lines, x-x, yy and zz, and a supposedwind current striking at the angle W have again been presumed and itwill be found that the same geometrical considerations prevail and theflue cap operates as effectively as before. The sectional view of Fig. 4has been taken along the diagonal line 4-4, this representing theextreme condition with respect to the presumed line x--x.

As to the number and spacing of the specially shaped apertured plates 14and 18 needed to accomplish the purposes of the invention, some generalrules can be stated. In the first place, configuration of the lowerplate sections must be such that no line similar to the line x-x can bedrawn which impinges below the inner edge of the flange of the lowermostplate which marks the bottom of the lowest air passageway from outsideinto the central cavity of the cap. In the embodiments shown anddescribed the result is accomplished by turning upwardly the innerflanges on the requisite number of lower plates 18. An engineer skilledin the art can readily compute the number, spacing, dimensions andconfiguration of plates 18 which will be required, once having beengiven the crosssectional area of the flue pipe 28 and the distancebetween the inner and outer edges of the plates.

The minimum number of plates 14 which should be mounted above the plates18 likewise can be determined as a practical matter, if not withmathematical exactness. As already stated, if down drafts werenon-existent, the ideal flue opening would be an unobstructed hole thesize of the flue, In the present invention I have provided a flue capwhich achieves the desirable results of eliminating the down drafts andproviding a covering against the elements while at the same timedeparting to the least possible extent from the ideal condition of anunobstructed hole. It. therefore, will be evident that the minimumnumber of plates 14 required is such, in view of their dimensions andmutual spacing, as to provide passages permitting the escape of air orgases very nearly as freely as if section 28 were uncapped, the diameterof section 28 being substantially the same as that of the flue to becapped. ln practice I have found that the' number of upper plates andtheir spacing should probably define a total passageway considerably inexcess of the theoretical minimum, this to accommodate some additionalvolume-of air which enters the device all along one side whenever thereis an external draft. A flue cap with somewhat less than the theoreticalminimum number of plane plates 14, although operating imperfectly,nevertheless in some conditions might perform the primary function ofthe invention, namely, to prevent down drafts. Elimination of all orsubstantially all of the plates 14 would produce substantialinterference with the free flow of escaping air or gases andconsequently the advantages according to the invention could not beattained. In view of their dimensions, their spacing should be such asto comply with. the rule already stated as to the maximum permissibleangle of the line x--x or a similar line. Likewise, I have found thatexcellent results can be obtained when the radius of the centralopenings in the plate 14 is approximately equal to the radius of aflange 22. In any event the lowest of the plane plates 14a should havean opening whose radius is at least equal to about this amount to permitpassage of air between it and the uppermost plate 18.

While I have herein disclosed and described presently preferredembodiments of the invention, it will nevertheless be understood, asabove indicated, that the same is susceptible of numerous modificationsand changes nevertheless within the scope of the appended claims. Thusthe number, dimensions, spacing and configuration of the various typesof plates may be altered within the limits indicated while adhering tothe principle of operation. Furthermore, the shape of the plates ascircular, square or otherwise, is unimportant so long as at the extremeof any dimensions the limiting angles hereinabove set out are observed.Particularly with respect to the shape of the one or more componentsforming the lower plate section, it is clear that equivalent shapesperforming the same function may be substituted for the upturned flanges22, as for example tilting these plates inwardly and upwardly orproviding curved portions at different areas from the extreme inneredges. Accordingly, the invention is not limited by the specificembodiments herein disclosed and described but only by the proper scopeto be given the appended claims.

I claim:

1. A flue cap comprising a series of plates and mountings holding saidplates in generally horizontal, parallel spaced relation, all but theuppermost of said plates having generally aligned openings correspondinggenerally in area to the cross-sectional area of the flue to be cappedand forming an internal cavity in said cap, said plates defining betweentheir opposing surfaces a series of air passageways between said cavityand the exterior of said cap, a sufficient number of the lowermostplates having their inner edges turned upwardly so that no unobstructedinwardly extending straight line may be drawn touching the outer edge ofany plate and the inner edge of the next lower plate and reaching apoint below the lowermost air passageway between said cavity and theexterior of said cap, the remaining plates having substantially planesurfaces, said cap having a portion at its bottom for attaching it to aflue.

2. A flue cap comprising a series of plates, and mountings holding saidplates in generally horizontal,

parallel spaced relation, said plates forming upper and lower platesections, all but the uppermost of said plates having central openingscorresponding generally in area to the cross-sectional area of the flueto be capped and forming an internal cavity in said cap, said platesdefining between their opposing surfaces a series of air passagewaysbetween said cavity and the exterior of said cap, a sufficient number ofindividual plates of the lower plate section having inwardly andupwardly projecting portions whose upper edges extend'at least as highas the plane of the bottom surface of the individual plates nextuppermost so that no unobstructed inwardly extending straight line maybe drawn touching the outer edge of any plate and the inner edge of thenext lower plate and reaching a point within said cavity below thelowermost air passageway between said central cavity and the exterior ofsaid cap, the plates of the upper section having substantially planesurfaces, said lower section having a mounting portion for attachingsaid cap to a flue.

3. A flue cap comprising a series of plates, said plates having alignedmounting holes, and mounting elements fitting said holes and spacersthereon holding said plates in generally horizontal, parallel spacedrelation, said plates forming upper and lower plate sections, all butthe uppermost of said plates having central openings correspondinggenerally in area to the cross-sectional area of the flue to be cappedand forming an internal cavity in said cap, said plates defining betweentheir opposing surfaces a series of air passageways between said cavityand the exterior of said cap, a suflicient number of individual platesof the lower plate section having inwardly and upwardly proj ectingportions whose upper edges extend at least as highas the plane of thebottom surface of the individual plates next uppermost so that nounobstructed inwardly extending straight line may be drawn touching theouter edge of any plate and the inner edge of the next lower plate andreaching a point within said cavity below the lowermost air passagewaybetween said central cavity and the exterior of said cap, the plates ofthe upper section having substantially plane surfaces.

References Cited in the file of this patent UNITED STATES PATENTS417,415 Esperson Dec. 17, 1899 855,710 Kayser June 4, 1907 FOREIGNPATENTS 115,483 Germany Nov. 28, 1900 407,427 Great Britain Mar. 22,1934 423,724 Great Britain Feb. 6, 1935

